This invention relates to a wheel-tire assembly for use on a ground vehicle (e.g. a military truck) operating on soft or hard terrain over a range of vehicle speeds. The wheel-tire assembly is designed so that when the vehicle is moving in a relatively low speed range (e.g. below fifteen miles per hour) the tire is in a partially deflated condition; when the vehicle is operating in a relatively high speed range (e.g. above thirty miles per hour) the tire is fully inflated. In an immediate speed range (e.g. between fifteen miles per hour and thirty miles per hour) the tire can be at progressively higher states of pressurization, i.e. a relatively low pressure at fifteen miles per hour gradually increasing to a relatively high pressure at thirty miles per hour.
The described variable tire pressure provides a relatively large area tire footprint at low vehicle speeds, and a relatively low area tire footprint at the higher vehicle speeds. A large area footprint is advantageous when the vehicle is operating in soft terrain, such as mud, snow or sand; during such periods the vehicle is usually moving at a relatively slow speed so that an increased area footprint is advantageous for traction purposes. When the vehicle is operating on hard dry surfaces at higher rates of speed the small area tire footprint provides decreased rolling resistance and better fuel economy; the higher inflation pressure and smaller tire footprint also tends to improve vehicle stability and controllability at medium and high vehicle speeds.
Under the present invention the desired variation in tire pressure is achieved by a system of valves mounted on the wheel. The wheel is preferably manufactured with a drop center rim to provide a protected cavity for the valves, especially when the tire is undergoing deflection in the partially flattened mode of operation.
The valves are designed so that during certain operational modes the valves cause atmospheric air to be introduced to the tire and exhausted out of the tire as a function of centrifugal force generated by the rotating tire-wheel assembly. At relatively low vehicle speeds a low centrifugal force condition causes reduced (or zero) quantities of air to be admitted to the tire. At intermediate vehicle speeds significant quantities of air are admitted to the tire to achieve higher inflation pressures. At higher vehicle speeds the tire is fully inflated; no air is admitted to the tire or exhausted out of the tire.
One object of the invention is to automatically achieve a relatively large tire footprint at low vehicle speeds and a relatively small tire footprint at high vehicle speeds.
Another object of the invention is to provide a variable tire air pressure, without the requirement for a complex air pressure source and air distribution system, e.g. a central air compressor and valved supply-exhaust lines traversing pneumatic slip rings on the wheels.